This application for a K25 Research Career Award, entitled "Optical Investigation of Excitation-Secretion coupling in Mammalian Peptidergic Nerve Terminals," describes the research and career development plan of Dr. Martin Muschol. The project will be mentored by Dr. Brian M. Salzberg and performed in his laboratory at the Dept. of Neuroscience of the University of Pennsylvania. The long-term career goal of this application is to provide Dr. Muschol with the necessary re-training to become an independent investigator in the biomedical sciences, who will identify and formulate relevant research questions in neuroscience, and address them with the means of advanced optical techniques. The immediate career goals are (a) to utilize his expertise with light scattering and optics to study intracellular events of exocytosis; (b) to expand his repertoire of optical techniques relevant to cell physiology; (c) to familiarize himself with biological preparations and standard biomedical assays; (d) to receive supplementary tutoring in neuroscience and neurobiology. The applicant's mentor, Dr. Brian M. Salzberg, is a widely respected expert in the field of optical probes and optical techniques and will act as a facilitator of these career goals. The proposed research project focuses on optical methods for studying excitation-secretion coupling in mammalian nerve terminals. The main purpose is to identify and characterize the intraterminal events leading from calcium entry to exocytosis. In the mammalian neurohypophysis, such early events of exocytosis manifest themselves in an intrinsic optical change (IOC). A clear identification of the physiological origin of the secretion related components of the IOC has proven challenging. One specific aim of the research project is to apply angular-resolved light scattering measurements in order to determine the intraterminal compartments and processes participating in the IOC. The second specific aim is to characterize the kinetics of intraterminal calcium changes greater than[Ca 2+], under physiological stimulation conditions. The role of different regulatory pathways of calcium regulation in shaping greater than[Ca 2+] will be determined. Specifically, the potential role of synaptic granules themselves in regulating intraterminal calcium during exocytosis will be investigated.